Zootaxa 4702 (1): 107–113 ISSN 1175-5326 (print edition) https://www.mapress.com/j/zt/ Article ZOOTAXA Copyright © 2019 Magnolia Press ISSN 1175-5334 (online edition) https://doi.org/10.11646/zootaxa.4702.1.15 http://zoobank.org/urn:lsid:zoobank.org:pub:8A8FD64D-DE1B-4379-BC96-D71AD0C43B04 A new Portholefish of the genus Diplophos (Stomiiformes: Gonostomatidae) from the western Pacific Ocean KEITA KOEDA1* & HSUAN-CHING HO1,2 1National Museum of Marine Biology & Aquarium, 2 Houwan Road, Checheng, Pingtung 94450, Taiwan 2Institute of Marine Biology, National Dong Hwa University, 2 Houwan Road, Checheng, Pingtung 94450, Taiwan *Corresponding author. E-mail: [email protected] Abstract A new Portholefish, Diplophos vicinia sp. nov., is described on the basis of nine specimens collected from the western Pacific Ocean by commercial midwater trawl. The new species, currently known only from the South China Sea and north of Papua New Guinea, can be easily distinguished from six nominal congeners by the combination of the following characters: dorsal-fin origin closer to snout than caudal-fin base, distance between last two AC photophores half that between preceding photophores, gill rakers 4 + 10–11=14–15, abdominal vertebrae 30–32, caudal vertebrae 44–45, total vertebrae 74–76, and the following photophore counts: IP 13–14, PV 18–19, IV 31–32, VAV 12–13, AC 37–39 + 2, and IC 83–86. Keywords: Diplophos vicinia, taxonomy, morphology, luminescence, deep sea, South China Sea Introduction The portholefish family Gonostomatidae is a group of mesopelagic marine fishes, represented by about 8 genera and 33 valid species (Nelson et al. 2016; Fricke et al. 2019). Species of the genus Diplophos are characterized by the following: dorsal-fin origin well anterior to anal-fin origin; photophores present on isthmus; more than 2 rows of photophores on body, VAV 12–17, IV 30–49, AC 28–49 (straight), IC 70–119, OA 45–87, BR 8–16; ORB pho- tophore below or slightly anterior to front margin of eye; lower gill rakers 7–10; upper and lower jaws uniserial, except for short outer row anteriorly; a row of small photophores on posterior half of lower jaw; single tooth row on premaxillary; and pseudobranchiae present (Grey 1960, 1964; Fujii 1984; Schaefer et al. 1986). Six nominal species [D. australis Ozawa, Oda & Ida 1990, D. orientalis Matsubara 1940, D. pacificus Günther 1889, D. proximus Parr 1931, D. rebainsi Krefft & Parin 1972, and D. taenia Günther 1873] are currently recog- nized in Diplophos (Fricke et al. 2019), although D. pacificus, known only from a single poorly preserved specimen, is probably invalid according to Ozawa et al. (1990). Ozawa et al. (1990) reviewed the systematics of the Diplophos taenia species complex, characterized by the last two AC photophores grouped together (all of the above species except for D. rebainsi), and described their morphological characters on the basis of the types and many additional specimens collected circumglobally. During a recent ichthyofaunal survey of the waters off southwestern Taiwan, two specimens of Diplophos with the last two AC photophores grouped were obtained at the Dong-gang fish market. Five additional specimens from the same market, and two others from the South China Sea and waters north of Papua New Guinea were found subsequently in museum collections. With meristic characters clearly unique within the genus, the specimens were recognized as a new species, which is formally described below. Methods and materials All measurements were made on the left side using digital calipers and rounded to the nearest 0.1 mm. Standard and head lengths are abbreviated as SL and HL, respectively. Rays of vertical fins and vertebrae were counted from Accepted by E. Hilton: 12 Sept. 2019; published: 4 Dec. 2019 107 Licensed under a Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0 radiographs. Terminology of photophores, and methods for counts and measurements follow Ozawa et al. (1990). Photophore descriptions were mostly based on the holotype (due to the poor condition of the skin and photophores in all remaining type specimens; the precise arrangement of accessory photophores was unclear and therefore their counts were deduced from the few remaining traces). Descriptions of fresh coloration were based on color photo- graphs of the holotype and one paratype (NMMB-P27286, 100.5 mm SL). The type series of the new species is deposited in Biodiversity Research Center, Academia Sinica, Taipei (ASIZP) and the fish collection of the National Museum of Marine Biology & Aquarium, (NMMB-P). Taxonomy Diplophos vicinia sp. nov. English name: Neighbor Portholefish Figures 1–3; Tables 1–2 Holotype. NMMB-P29097, 127.6 mm SL, off Dong-gang, Pingtung, South China Sea, Taiwan, 21 Mar. 2018, ob- tained at fish-landing ground at Dong-gang; collected by commercial mid-water trawl. Paratypes. Collection locality and method same as holotype: ASIZP 64190, 2 specimens, 84.4–95.0 mm SL, 24 Mar. 2004; NMMB-P9246, 99.7 mm SL, NMMB-P30714, 101.9 mm SL, 18 Sept. 2008; NMMB-P11930, 129.7 mm SL, 28 Feb. 2011; NMMB-P27286, 100.5 mm SL, 14 Oct. 2017. South China Sea (22°04ʹN, 120°27ʹE): ASIZP 64180, 73.9 mm SL, 25 March 2004. Between Papua New Guinea and Micronesia (02°42ʹN, 150°03ʹE): ASIZP 73845, 143.5 mm SL, 27 August 2010. FIGURE 1. Type specimens of Diplophos vicinia sp. nov. in fresh condition. Top: NMMB-P29097, 127.6 mm SL, holotype from southwestern Taiwan; bottom: ASIZP 73845, 143.5 mm SL, paratype from between Papua New Guinea and Micronesia (photo taken by M.-Y. Lee). FIGURE 2. Radiograph of holotype of Diplophos vicinia sp. nov. (NMMB-P29097, 127.6 mm SL). Diagnosis. A species of Diplophos with the following combination of characters: anal-fin rays 57–59; bran- chiostegal rays 14; gill rakers 4 + 10–11=14–15; abdominal vertebrae 30–32; caudal vertebrae 44–45; total ver- tebrae 74–76. Photophores: IP 13–14, PV 18–19, IV 31–32, VAV 12–13, AC 37–39 + 2, IC 83–86; last two AC 108 · Zootaxa 4702 (1) © 2019 Magnolia Press KOEDA & HO photophores grouped, separation less than half that of preceding photophores; dorsal-fin origin closer to snout than caudal-fin base, pre-dorsal-fin length 45.2–47.3% SL. Description. Counts and measurements are given in Tables 1 and 2. The following data are given for the holo- type, with values of paratypes in parentheses, unless otherwise indicated. Body strongly elongated, its greatest depth (usually at base of pelvic-fin) 10.3 (8.7–13.8) in SL; dorsal and ventral outlines almost straight along abdomen, gradually becoming shallower along tail. Body and head strongly compressed laterally, progressively more so toward the caudal peduncle; snout to anus less than half body length. Scales on body lost in all specimens. TABLE 1. Meristic data of the type series of Diplophos vicinia sp. nov. and D. taenia. D. vicinia D. taenia Holotype Paratypes Non-type NMMB-P29097 n=8 ASIZP 75043 Standard length 127.6 73.9–143.5 114.5 Counts Dorsal-fin rays 12 11–12 10 Anal-fin rays 57 57–59 damaged Pectoral-fin rays 10 9–10 9 Pelvic-fin rays 8 8 8 10 + 9 Caudal-fin rays 10 + 9 10 + 9 Branchiostegal rays 14 14 14 Gill rakers 4 + 10=14 4 + 10–11=14–15 3 + 9=12 Abdominal vertebrae 30 30–32 38 Caudal vertebrae 44 44–45 55 Total vertebrae 74 74–76 93 Photophores IP 13 13–14 19 PV 18 18–19 22+ IV 31 31–32 41+ VAV 13 12–13 17 AC 37 + 2=39 37–39 + 2=39–41 damaged IC 83 83–86 N/A OV 18 18–19 25+ VALA 13 12–13 16 OAA 31 31–32 41+ VALB 17 17–19 28 OAB 48 48–50 69+ BR 11 11–12 12 Head small, 6.6 (6.0–6.8) in SL; snout short, moderately pointed, its length greater than eye diameter. Eye moderately large, circular, its diameter 4.1–5.0 in HL. Olfactory laminae inside nostril 21–23, visible externally. A NEW DIPLOPHOS FROM TAIWAN Zootaxa 4702 (1) © 2019 Magnolia Press · 109 Mouth large, weakly oblique, ventral margin of maxilla strongly curved, posteriorly nearly reaching the margin of preoperculum. Single row of large caniniform teeth on all jaws, one to three small sharp teeth between each large caniniform tooth; teeth present from near symphysis of premaxilla to posterior end of maxilla, largest on premaxilla, slightly larger than those on maxilla and dentary; single middle-sized tooth row on anterolateral aspect of dentary; two small conical teeth on vomer; single row of three to seven small conical teeth on palatine. Two small teeth on anterior part of basihyal. Four gill arches present, a well-developed slit behind fourth; gill rakers on first to third gill arches comb-like, but on fourth gill arche knob-like; lowermost upper gill raker and uppermost lower gill raker closely attached to each other. Pseudobranch small with 7 (3–10) short filaments. All fin rays short, transparent and fragile; dorsal-fin base short, originating anterior to origin of anal fin, ending slightly posterior to anal-fin origin; anal-fin base long, its length 7.4 (7.3–10.6) times dorsal-fin base length; pec- toral fin small, inserted level with posteroventral portion of gill slit; pelvic fin small, closer to anal-fin origin than closest point of pectoral-fin base; caudal fin small, its maximum length less than caudal-peduncle length. Head photophores (Fig. 3). Single supraorbital photophore (ORB) at anterodorsal corner of eye between eye and nostril, small, embedded under skin; 12 small photophores in horizontal series along ventral margin of eye; one large photophore below anteroventral portion of eye; 9 small photophores in horizontal linear series below middle of eye; one medium-sized photophore below posteroventral portion of eye; one large photophore (anteriormost one of OP) beneath middle of preopercle, followed by 6 small photophores in horizontal linear series along dorsal margin of premaxilla; one large photophore posterior to and just below dorsal margin of preopercle; 5 small photophores in vertical series beneath border of preopercle and opercle; 5 small photophores in longitudinal series beneath ventral margin of preopercle; 2 large elongated photophores (posterior two of OP) beneath border of subopercle and in- teropercle; two series of 5 or 6 small photophores on interopercle; single row of ca.